I'm not a historian, but doesn't this question have a few potentially unwarranted assumptions? Was the roman culture actually hard working? Is current Italian culture actually so licentious? Also did cultural behavors chamge or did just the cultural stereotypes change?

Assumptions aside the "Roman Ideals" were a self imposed narrative written by the early Romans. Some Romans may have held all of those ideal characteristics but for every one of those there were more that were the opposite. Where you really start to see it is when the Roman civil wars start up about 80 years before Cesar.

The faction in power would always try to portray their counterparts as morally corrupt as justification for their grab for power. The Republicans under Sulla consolidated power and forced the Democrats under Marius to flee Rome and killed those who did not flee. The civil war that followed had Sulla killing civilians, confiscating land and looting temples to pay for the war. Sulla died however reestablishing the senate as dominate in Roman politics. Marius' nephew in law Cesare, when he came to power had story after story published about when Sulla died his intestines erupted with worms and rot, Showing how morally bankrupt Sulla was. Cesare also made sure all negative portrayals of Marius disappeared.

This is pretty constant with all cultures through out time with few exceptions. Given the opportunity they will glorify themselves and disparage their adversaries.

To be honest, when picturing Romans, I picture the Roman military as an example, even do by the time of the Empire the roman elite and most of it citizens were far from virtuous. For me, the image of a hard working roman changed when the one got his hand on the endless amount of slave force, fine culture, cuisine and other stuff which made him abandon the idea of hard work for himself and enjoy the life as he gets - which pretty much started after the end of the Punic wars. Pretty much after the Rome was gone, there were no attempts from roman descendants to recreate the glorious empire for themselves on Italian peninsula, so I guess most people see these descendants as someone who failed to live up to the work of their ancestors (even do they are not really romans and the actual romans lived in a completely different climate).